Write checksums into a file for later use

[GoogleCodeExporter]

Add new option to write generated checksums in the pre-processing stage into a 
file. and reading them back in another program run.

This can speed up processing of very large source files repeatedly with many 
targets. Similarly, it can allow split processing of very large files into 
reasonable chunks using always the same large source and processing each chunk 
in a separate run.

Original issue reported on code.google.com by mantl...@gmail.com on 5 Aug 2013 at 11:48

[GoogleCodeExporter]

This issue was updated by revision b997364aaf8b.

Checksum save/restore to/from a file implemented.
New option -cf <file> added.
When checksum file does not exist, new file is created when preparation pass 
finished.
When checksum file exists, checksums are not computed, but loaded from the file 
instead.
No integrity check is provided. Using of file from other/modified source can 
lead to unpredictable results.

Original comment by mantl...@gmail.com on 5 Aug 2013 at 6:55

[GoogleCodeExporter]

This issue was updated by revision 20484b147101.

Improved progress reporting.

Original comment by mantl...@gmail.com on 6 Aug 2013 at 6:00